A push belt for a continuously variable transmission is generally known. Usually, such a push belt comprises two ring-shaped carriers for carrying a relatively large number of transverse elements. The carriers are like ribbons which are relatively thin in relation to their diameter. The transverse elements are arranged along the entire circumference of the carriers, wherein they are able to transmit forces which are related to a movement of the push belt.
For the purpose of receiving the carriers of the push belt, the transverse element is provided with recesses, at two sides, and for the purpose of supporting the carriers, the transverse element comprises carrying surfaces. Furthermore, for the purpose of contact between the transverse element and pulley sheaves of a pulley of a continuously variable transmission, the transverse element is provided with contact surfaces, at two sides, which are divergent with respect to each other in the direction of the carrying surfaces. The terms “top” and “bottom”, which are hereinafter applied, are related to the direction of divergence; this is defined as being from bottom to top.
From bottom to top, the transverse element comprises successively a basic portion, a middle portion and a top portion, wherein the dimensions of the middle portion are relatively small. The basic portion comprises the carrying surfaces and the contact surfaces. Normally, in the push belt, the basic portion is located at the side of the inner circumference of the push belt, whereas the top portion is located at the side of the outer circumference of the push belt.
The transverse element has two main body surfaces which extend substantially parallel with respect to each other. A correct position of a transverse element in a push belt is a position in which the main body surfaces are more or less perpendicular to the circumferential direction of the push belt. At least a portion of a first main body surface of the transverse element is destined to abut against at least a portion of a second main body surface of an adjacent transverse element in the push belt, whereas at least a portion of the second main body surface of the transverse element is destined to abut against at least a portion of the first main body surface of another adjacent transverse element in the push belt.
A circumferential surface, of which the carrying surfaces and the contact surfaces are part, extends between the two main body surfaces. Furthermore, the top portion comprises two retaining surfaces which are facing the carrying surfaces, and which are also part of the circumferential surface. In a push belt, the position of the carriers is delimited in a radial direction of the push belt by the carrying surfaces at one side, and by the retaining surfaces at another side.
On one of the main body surfaces of the transverse element, a projection is arranged, whereas in another of the main body surfaces of the transverse element, a recessed portion, which will hereinafter be referred to as depression, is arranged. The positions of the projection and the depression correspond to each other, wherein the projection and the depression are usually positioned on the top portion. In the push belt, the projection of every transverse element is at least partially located in the depression of an adjacent transverse element, so that a mutual displacement of the transverse elements in a plane perpendicular to the circumferential direction of the push belt is prevented.
In order to guarantee proper functioning of the push belt having the carriers and the transverse elements as described in the foregoing, and to realize optimal torque transmittal in a continuously variable transmission in which the push belt may be applied, there is a need for effective contact between the transverse elements of the push belt and the pulleys of the continuously variable transmission. In view of this need, the contact surfaces of the transverse elements are often provided with a corrugated or serrated profile. The profile may be such that there is a pattern of alternating elevations and recesses, particularly ribs and grooves, which are both extending from one side of the contact surfaces to another, in the circumferential direction of the push belt, in a substantially parallel arrangement.
Among other things, when the contact surfaces are provided with a profile, indeed, the profile serves for preventing the formation of an oil film between the contact surfaces of the transverse element and the pulley sheaves, as a result of which slipping of the push belt with respect to the pulleys is prevented. Another advantageous effect of the application of a profile on the contact surfaces of the transverse element is that small mutual differences in the dimensions of the transverse elements of a push belt may diminish during a process of running-in of push belt and pulleys, because the profile allows for a situation in which a small wear of the contact surfaces takes place at places where the differences are the largest. In other words, pulleys and push belt may show a slight initial wear with respect to each other, after which a good grip between the contact surfaces of the transverse elements of the push belt and the pulley sheaves results, and the push belt is guided along the pulleys in an exceedingly stable fashion.
In fact, when the profile on the contact surfaces of the transverse element comprises a pattern of alternating ribs and grooves, tops of ribs initially have a relatively small surface, and therefore may relatively easily wear away a little in case of contact to a pulley sheave, as a result of which dimensional variations between the various transverse elements in the push belt are leveled out. In EP 0 994 275, a number of profiles which are arranged at the contact surfaces of transverse elements are described, wherein a sine-shaped profile is presented as a preferred embodiment.
As the contact between a pulley sheave and transverse elements mainly takes place at the positions of the ribs of the profile, it is true that not the entire contact surface of the pulley sheave is involved in torque transmittal. It is an objective of the present invention to provide a solution according to which the contact surface of the pulley sheaves is used to a much larger extent, so that torque transmittal can be further optimized and wear can be reduced.